Low pressure abrasive blasting system

ABSTRACT

AN ABRASIVE BLASTING APPARATUS COMPRISING AT LEAST ONE NOZZLE FOR PRODUCING A RELATIVELY WIDE, SHEET-LIKE STREAM OF ABRASIVE PARTICLES INCLUDES AN ELONGATED NOZZLE HAVING A CONSTANT WIDTH BUT A THICKNESS THAT DIMINISHES FROM ITS INLET OT ITS OUTLET BY EITHER AN ABRUPT OR GRADUAL TAPER. A SOURCE OF RELATIVELY LOW PRESSURE AIR IS SUPPLIED TO THE NOZZLE AND NEAR ITS INLET A FEED HOPPER CONSTANTLY SUPPLIES ABRASIVE MATERIAL, BY DISTRIBUTING IT SUBSTANTIALLY UNIFORMLY ACROSS THE WIDTH OF THE AIR STREAM THAT ENTERS THE NOZZLE. THE LOW PRESSURE AIR ACCELERATES THE ABRASIVE PARTICLES TO A VELOCITY AT THE NOZZLE EXIT WHICH IS SUFFICIENT TO ACCOMPLISH THE SURFACE TREATMENT OF VARIOUS MATERIALS. THE NOZZLE MAY BE ORIENTED IN DIFFERENT POSITIONS AND ARTICULATED IN DIFFERENT WAYS TO ACCOMPLISH TREATMENT OF DIFFERENT FORMS OF WORKPIECES.

T. A. ARNOLD LOW PRESSURE ABRASIVE BLASTING SYSTEM Feb. 9, 1971 3 Sheets-Sheet 1 Filed Jan. 51; 1969 FIG 2g F|G 2 b INVENTOR. TED A. ARNOLD Feb. 9, 197.1 T. A. ARNOLD 3,561,163

LOW PRESSURE ABRASIVE BLASTING SYSTEM Filed Jan. 51, 1969 3 Sheets-Sheet 2 INVENTOR.

TED A. ARNOLD @m, WLM

ATTORNEYS T. A. ARNOLD LOW PRESSURE ABRASIVE BLASTING SYSTEM I Feb. 9, 1971 3 Sheets-Sheet 8 Filed Jan. 51. 1969 INVENTOR. TED A. ARNOLD ATTORNE'YS nited States Patent ()fice fornia Filed Jan. 31,1969, Ser. No. 795,544 Int. Cl. B24c 3/00 US. Cl. 51-8 12 Claims ABSTRACT OF THE DISCLOSURE An abrasive blasting apparatus comprising at least one nozzle for producing a relatively wide, sheet-like stream of abrasive particles includes an elongated nozzle having a constant width but a thickness that diminishes from its inlet to its outlet by either an abrupt or gradual taper. A source of relatively low pressure air is supplied to the nozzle and near its inlet a feed hopper constantly supplies abrasive material, by distributing it substantially uniformly across the width of the air stream that enters the nozzle. The low pressure air accelerates the abrasive particles to a velocity at the nozzle exit which is sufficient to accomplish the surface treatment of various materials. The nozzle may be oriented in different positions and articulated in different ways to accomplish treatment of different forms of workpieces.

This invention relates to abrasive blasting apparatus and more particularly to such an apparatus for continuously cleaning or treating surfaces with a relatively wide stream of abrasive.

In abrasive blasting wherein abrasive particles are entrained in an air stream and impinged against a metal surface for the purpose of peening or treating the metal or cleaning it by removing paint, dirt, scale or some other material, blasting systems heretofore devised operated under relatively high air pressure to produce a generally round stream of abrasive. This limited the area that could be covered by such nozzles and made it necessary to articulate the nozzle in order to cover or sweep relatively large areas. Previous attempts to shape nozzles from a round throat to one having a long-sided, narrow-rectangular outlet to provide a wider stream of abrasive were unsuccessful for various reasons. One problem which arose was a difficulty in producing an even distribution of abrasive across the full width of the nozzle outlet. Another problem was in reducing the large power requirements of maintaining a high flow of abrasive particles at the high velocity required to obtain the proper abrasive action. A general object of the present invention is to provide solutions to these problems, and more particularly to provide an abrasive blasting system that will produce a relatively wide but narrow stream of high velocity abrasive particles with a substantially uniform distribution across the full width of the nozzle.

Another object of the present invention is to provide an abrasive blasting system for producing an evenly distributed flow of abrasive across the width of a generally rectangular shaped nozzle having a relatively long and narrow slot-like opening and which is equally effective for relatively large nozzles with high volumes as well as small nozzles and at either relatively high or low operating pressure.

In accordance with the present system the abrasive material is metered into the nozzle at a point from its exit opening where the width of the conveying air stream is the same as and does not change until it reaches the nozzle exit. The other dimension of the nozzle does decrease to a minimum at some point along the nozzle be- 3,561,163 Patented Feb. 9, 1971 tween the metering point and the nozzle exit in order to increase the air velocity above a mere conveying velocity, thereby accelerating the abrasive particles to the speed necessary to per-form effective blasting or peening. In order to get an even and consistent flow of abrasive through the slot-like nozzle opening I have discovered that an abrasive feeding means must be provided that applies abrasive to the air stream at or near the nozzle input and in a uniform quantity along a line across the nozzle width. In addition, the nozzle must have a length that is sufficient to enable the abrasive particles to accelerate to the speed required for blasting efliciency.

Yet another object of my invention is to provide an abrasive blasting system for removing scale dirt or other deleterious material or to surface treat simultaneously both sides of a strip of metal that is moved between a pair of nozzles, one directed upwardly and the other downwardly with their elongated openings being located transverse to the direction of travel of the strip.

Other objects, advantages and features of my invention will become apparent from the following description presented in conjunction with the drawings, in which:

FIG. 1 is a view in elevation showing a strip cleaning abrasive blasting apparatus embodying the principles of the present invention;

FIG. 2 is an enlarged fragmentary view in perspective showing the dual nozzle arrangement on the apparatus of FIG. 1;

FIG. 2a is an enlarged view in side elevation showing one form of nozzle for use with my apparatus;

FIG. 2b is an enlarged view in side elevation showing another form of nozzle according to my invention;

FIG. 3 is an enlarged fragmentary view in perspective showing a modified feed system for the upper nozzle of the dual nozzle arrangement of FIG. 2;

FIG. 4 is an enlarged fragmentary view in perspective showing another modified feed for the upper nozzle of the dual nozzle arrangement of FIG. 2;

FIG. 5 is another fragmentary view in perspective showing a single nozzle arrangement according to the present invention oriented horizontally to treat vertical surfaces;

FIG. 6 is an enlarged fragmentary view in perspective showing a modified feed system for the lower nozzle of the dual nozzle arrangement of FIG. 2;

FIG. 7 is an enlarged view in elevation and in section showing a feed valve for feeding abrasive material into a nozzle according to my invention; and

FIG. 8 is a plan view of the feed valve of FIG. 7.

Referring to the drawing, FIG. 1 shows one form of an apparatus 20 embodying the principles of the present invention which will produce a relatively wide stream of abrasive material and is particularly adaptable for removing dirt, scale, or a layer of metal from one or both sides of a workpiece such as a sheet metal strip. Generally, the apparatus comprises an upper nozzle 22 and a lower nozzle 24 whose outlets are spaced just above and below the strip of material being treated, which is indicated by the numeral 26. This strip material is preferably fed through the apparatus at a constant linear speed. The lower nozzle 24 is oriented vertically and for convenience may be located in a pit 28 that extends below the floor level. The upper nozzle 22 is also oriented vertically and aligned with the lower nozzle with its outlet open downwardly. The two nozzles are preferably enclosed in a housing 30 to retain the abrasive and debris in a confined area so that it can be removed by an air conveying system. The spent abrasive and debris particles are preferably collected in a ducted floor 32 at the bottom of the pin and conveyed upwardly to a suitable cyclone separator 34 or an air wash system that removes the abrasive from the debris and conveys it to a storage hopper 36 for reuse.

The dust and debris from the separators is conveyed from the separators to a series of storage containers 38 which may be periodically emptied.

The air for propelling the abrasive particles in a blasting stream is provided from a blower 40 at a relatively low pressure (e.g. to p.s.i.) to a pair of conduits 42 that are connected to the nozzles 22 and 24. Thus, in these conduits leading to the nozzles, a relatively large volume of air travels at a fairly low velocity until it reaches the inlet end of the nozzle.

Each nozzle is relatively long and tapers from a maximum thickness at its inlet 44 to a lesser thickness somewhere between its inlet and its outlet 46 so that the air velocity within the nozzle increases accordingly. For example, as shown in FIG. 2a the nozzle 22 may taper gradually along its length from its inlet to near its outlet. However, in some instances, as shown in FIG. 2b I may provide a nozzle 23 with an abruptly tapered section 25 followed by a relatively long section 27 having a constant thickness. In either case, at its inlet, each nozzle in my apparatus has a rectangular shape in cross section and as the nozzle extends towards its outlet, its width (which is the length of the air passage cross section) remains constant but its thickness (the smaller dimension of this nozzle cross section) decreases at some point to a minimum dimension. Thus, the nozzle outlet opening is relatively narrow and due to the nozzle taper the air velocity increases considerably within the nozzle. In order to accelerate the abrasive particles to the exit velocity necessary to enable the particles to perform their surface treating function, I have found that the nozzle length, operating in the low pressure region of my system, should be in the order of 3-6 feet in length. The width of the nozzle at its inlet should be in the range of 6 to 200 times the nozzle thickness for best results. I have discovered that particularly good results are obtained when the thickness of the nozzle at its inlet is between one quarter and one inch.

The abrasive material useable in the apparatus of the present invention may be of any various well known types such as glass beads or steel shot ranging from 10 to 1,000 microns. The abrasive is fed from some suitable storage device to the large inlet end of each nozzle, and preferably it is fed under pressure so that it flows evenly into the nozzle. In the arrangement shown in FIGS. 1 and 2, the abrasive is fed from a first pressure pot 48 located beneath the storage hopper 36 that collects the spent abrasive from the cyclone separator 34 and then to a second feed pot 50 in the conventional manner. From the second pot the abrasive is carried by conveying air through a pair of conduits 52 and 54 to the inlet ends of the nozzles 22 and 24.

In another abrasive feeding arrangement, as shown in FIG. 3, the abrasive is first supplied to an intermediate storage hopper 56 which is located above the level of the nozzle inlet. This storage hopper has a normally closed inlet 58 through which it can be periodically charged with abrasive material, and preferably this hopper is connected by a small conduit 60 to the main air duct 42. When the storage hopper has been filled with abrasive by some suitable means the conduit 60 supplies it with air pressure during the operation of the system, thereby forcing abrasive to the nozzle at a constant rate.

In the embodiment of FIG. 2 utilizing a pressurized feeding arrangement, the end of the conduit 52 for the upper nozzle 22 is connected by means of a suitable adaptor fitting 62 to a feed inlet section 64 that has a constant width and connects with an air duct section 66 of the same width fixed to the nozzle inlet. At the end of the conduit 54 for the lower nozzle 24, a similar feed inlet section 64a has a constant Width but curves upwardly to connect with a duct section 66a.

The manner in which the abrasive material is delivered from the inlet section 64 into the air stream within the duct 66 that enters the nozzle is a critical factor in producing a uniform flow of abrasive across the width of the nozzle outlet. Whether the nozzle is directed downwardly as nozzle 22 or upwardly as with nozzle 24, the abrasive must be substantially evenly distributed across the width of the airstream entering the nozzle. If so, it will exit from the nozzle in essentially the same evenly distributed pattern across the nozzle width.

Various forms of feed valves may be utilized to provide the aforesaid even distribution of abrasive material into the airstream. One such feed valve 68 is shown in FIGS. 7 and 8 fixed to one sidewall of an air duct section 66 at a slot 70 that extends across the entire width of\ this duct section. A valve inlet connected to some abrasive supply has sidewalls 72 that converge toward each other on opposite sides of the slot and these sidewalls are fixed to but spaced from the slot of the air duct 66. Interconecting the inner edge of each converging sidewall 72 and the duct on opposite sides of the slot 66 are a pair of flexible valve members 74 of some suitable elastomeric material. Each valve member is bent in a U-shape with an outer end portion fixed to an inlet sidewall and an inner end portion fixed to the adjacent wall of the duct 66. Between the end portions of each valve member is a control rod 76, and both rods extend parallel to the slot 70 in the air duct. The rods are movable towards and away from each other and in so moving they flex the elastic valve members 74 to vary the size of the feed valve opening adjacent the slot, thereby varying the amount of abrasive flowing through the slot 70 into the duct section 66 across its entire width.

In the arrangements shown, the control rods 76 are connected to a suitable linear actuator that is operable to move the rods to a predetermined position to control the flow of abrasive. One control rod is connected by a U- shaped bracket 78 to a piston 80 of the actuator and the other control rod is connected by a similar but larger bracket 82 to the cylinder portion 84 of the actuator. A plurality of adjustable stop members 86 each mounted in a support 88 fixed to the wall of the air duct section 66, serve to control the amount of travel of the brackets 78 and 82 and thus the limits of the size of opening provided by the rods 76 of the feed valve. From the aforesaid description and the drawing it is apparent that when the piston is forced to move out of its cylinder, the opening of the valve will become smaller and vice versa. Although this pinch type feed valve is particularly adaptable to my system, other forms of feed valves could be used within the scope of the invention to provide the uniform flow of abrasive into the air stream.

The enlarged fragmentary views of FIGS. 2-6 illustrate alternative nozzle arrangements for various forms of apparatus embodying the principles of the present invention. FIG. 2, for example, shows the arrangement of FIG. 1 in which the two nozzles 22 and 24 are utilized for treating both sides of a workpiece simultaneously. Here, the air ducts 42 from the blower 40 are cylindrical pipe, and near each nozzle they are connected by a tapered adaptor 90 to a duct section 92 having a constant rectangular cross section. The latter curves from the end of the adaptor and is connected to the duct section 66 at the inlet of the nozzle. At this junction with the duct section, a feed valve 68 such as previously described, provides an even distribution of abrasive into the air stream. In FIGS. 2-6, the feed valve is not shown in detail in order to simplify the drawings, but its location is indicated by the numeral 68.

While the apparatus 20, as shown in FIGS. 1 and 2 utilizes two nozzles and is, therefore, capable of treating two surfaces simultaneously, it is apparent that only one nozzle could be used, if desired. In FIG. 3 a single nozzle 22a is shown having an inlet duct section 66a which is connected through an adaptor 90a directly to an air duct 42a that approaches the nozzle at a right angle. At the inlet section a feed valve inlet 94 having a constant width and converging sidewalls is connected by a conduit 96 to an intermediate supply hopper 56 that is pressurized from the main air conduit by the smaller conduit 60 connected thereto.

In FIG. 4, the arrangement shown is similar to that of FIG. 3 except that a main air duct 42b is vertically oriented and thus aligned with the longitudinal dimension of the nozzle 22b. A suitable means such as an actuator 98 may be supplied to rotate the nozzle about its longitudinal dimension, thereby enabling it to be turned with respect to the workpiece and treat surfaces having a width that is narrower than the nozzle. Here, an intermediate supply hopper 56b is shown connected directly to an inlet 94b and thence to a feed valve 68 in an inlet duct section 66b. A pressurizing air tap conduit 60b is connected to the storage hopper 56b in the same manner as previously described.

In FIG. 5, a slightly diiferent arrangement is shown for a nozzle 220 according to my invention which is mounted horizontally. An inlet duct section 660 attached to the nozzle is connected to an air pressure source such as a blower 40c (shown in phantom). An intermediate sup ply hopper 56c connected to a suitable abrasive feed valve at 68 is supplied with air pressure through a conduit 600, as previously described. Here, the nozzle 220 is connected by a hinge 100 extending across the full width of the inlet section which has a rectangular cross section. A suitable actuator means, shown schematically at 102, such as a controllable hydraulic actuator, may be provided for moving the nozzle back and forth within angular limits (e.g. 15 above and below a horizontal position), thereby enabling to provide increased angular coverage on a workpiece that is either held stationary or moved near'the outlet of the nozzle.

FIG. 6 illustrates another arrangement for an upwardly extending nozzle 24a. Here, a U-shaped inlet duct section 104 having a uniform rectangular cross section is connected to a typical air duct 42. by an adaptor 90. A feed valve 68 and ah inlet thereto is mounted on an intermediate horizontal portion of the inlet section 104 and is connected by a conduit 106 to an abrasive supply hopper 56d which may or may not be pressure boosted by air from the main duct in the same manner as previously described with re spect to FIGS. 3-5. The arrangement shown here differs from the lower nozzle setup of FIGS. 1 and 2 in that it allows the abrasive to be fed essentially by gravity under ideal conditiops and also affords greater travel of the abrasive material in the airstream before it enters the nozzle. However, with the abrasive in the airstream as it turns upward to eriter the nozzle, some additional wear may occur on the outer wall of the inlet section. Thus, to reinforce this portion of the inlet section a strengthening member 108 may be attached to the outer wall at this location.

An apparatus embodying the principles of the present invention, such as the apparatus 20, may utilize two nozzles 22 and 24 or it may use only one nozzle. In the apparatus the. workpiece being treated may be held stationary or it may be moved in some manner beneath the nozzles. In FIGS. 2-6 the lines in phantom indicate one obvious orientation of a workpiece and illustrates the fact that the present invention is particularly adaptable for treating the surfaces of long strips and the like. If desired, the nozzles themselves may be articulated to some limited degree to increase their area of coverage. Thus, the present invention provides a unique versatility and may be applied in a wide variety of arrangements, all of which utilize a relatively wide, fan-like abrasive blasting pattern that utilizes relatively low pressure air to accelerate the abrasive material to an adequate blasting velocity. v

To those skilled in the art to which this invention relates, many changes in construction and widely dilfering embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. An abrasive blasting system for producing a relatively wide stream of abrasive particles against a workpiece comprising:

-blower means for providing a constant How of air at a uniform pressure;

a conduit connected to said blower means;

an intermediate conduit section connected to said conduit and having a substantially rectangular crosssection;

an elongated nozzle having an inlet end fixed to said intermediate conduit section, said nozzle having a constant width and a rectangular cross-section throughout its length, the thickness of said nozzle being small in comparison to its width and decreasing from a maximum dimension at its inlet to a minimum dimension between its inlet and its outlet; and

feed means for dispensing abrasive material into said intermediate conduit section at a substantially uniform rate along a line extending transversely across the full width of said nozzle near its inlet.

2. The blasting system as described in claim 1 wherein the width of said nozzle at its inlet is in the range of 6 to 200 times the nozzle thickness.

3. The blasting system as described in claim 1 wherein the thickness of said nozzle at its inlet is between onequarter and one inch.

4. The blasting system as described in claim 1 including means for supporting said nozzle in a vertical position so that it can direct the wide stream of abrasive particles against a workpiece below the nozzle outlet.

5. The blasting system as described in claim 1 including means for rotating said nozzle about its longitudinal axis.

6. The blasting system as described in claim 1 wherein said nozzle has a length between 3 and 6 feet.

7. The blasting system as described in claim 1 including a second intermediate conduit section connected to said conduit from said blower means; a second elongated nozzle connected to said second intermediate conduit section and also having a constant width with a thickness that decreases from its inlet to its outlet end; means for supporting said second nozzle vertically with its outlet uppermost from its inlet and thereby directing a wide stream of abrasive upwardly; and feed means for dispensmg abrasive material into said second intermediate condult section along a line extending transversely across the width of said second nozzle near its inlet end.

8. The blasting system as described in claim 1 including a supply container for abrasive material; means for supplying air pressure to said supply container; and a feed conduit extending from said supply container to said feed means. 9. The blasting system as described in claim 8 wherein said supply container for abrasive material is located above said nozzle and said means for supplying air pressure thereto comprises a conduit means connected from said supply container to said conduit from said blower means.

10. The blasting system as described in claim 1 including means for supporting said nozzle so that its longitudinal and transverse axes are in a horizontal plane.

11. The blasting system as described in claim 10 including means for oscillating said nozzle up and down between predetermined angular limits while it is dispensing a wide stream of abrasive material.

12. The blasting system as described in claim 1 wherein said feed means includes a slot extending transversely across said intermediate conduit section; a pair of valve members fixed to opposite sides of and extending parallel to said slot; and means for moving said valve members closer together or further apart to vary the size of the opening and provide an even flow of abrasive material 2,524,097 10/1950 Barr et a1. 51-8 into said intermediate conduit section across its width. 2,605,596 8/1952 Uhri 51-11X 3,150,467 9/1964 Umbricht et a1. 51--11X References Cited UNITED STATES PATENTS 5 LESTER M. SWINGLE, Primary Examiner 250,185 11/1881 Atkins 5114 C 365,261 6/1887 King et a1 51-14 51 11 14 1,125,232 1/1915 Weyl 51319 

